Paul was under the inspiration of the Holy spirit, so saying that he thought Jesus would come in his life time is just wrong; it is like saying the Holy spirit thought.... Paul knew very well what he was talking about, a few chapters before that, Paul told Corinthians the opposite of that:
2 Cor 4:
10We always carry around in our body the death of Jesus, so that the life of Jesus may also be revealed in our body.
11For we who are alive are always being given over to death for Jesus’ sake, so that his life may also be revealed in our mortal body.
12So then, death is at work in us, but life is at work in you.
13It is written: “I believed; therefore I have spoken.”
b Since we have that same spirit of
c faith, we also believe and therefore speak,
14because we know that the one who raised the Lord Jesus from the dead will also raise us with Jesus and present us with you to himself. 15All this is for your benefit, so that the grace that is reaching more and more people may cause thanksgiving to overflow to the glory of God.
Paul here is counting himself amongst the dead who will be raised and be caught up together with his listeners at corinth who will be alive.
It is not Paul who thought..., it is the understanding of many that fails and the result is the popular but wrong theology around resurrection/Rapture/Christ/end times/eschatology. The resurrection is not what many think it is, it is not a mass event at some day in the future, resurrection is now and is continuous - this is what Paul taught.
From the verses below, i know that Paul is talking about some continuous process as opposed to a future event because he carefully chooses the tense; he doesn't use future tense but continuous tense:
1 Cor 15:
12But if it is preached that Christ has been raised from the dead, how can some of you say that there is no resurrection of the dead?
13If there is no resurrection of the dead, then not even Christ has been raised.
14And if Christ has not been raised, our preaching is useless and so is your faith.
15More than that, we are then found to be false witnesses about God, for we have testified about God that he raised Christ from the dead.
But he did not raise him if in fact the dead are not raised. 16For if the dead are not raised, then Christ has not been raised either.
17And if Christ has not been raised, your faith is futile; you are still in your sins.
18Then those also who have fallen asleep in Christ
are lost.
19If only for this life we have hope in Christ, we are of all people most to be pitied. .....
29Now if there is no resurrection, what will those do who are baptized for the dead? If the dead are not raised at all, why are people baptized for them?
30And as for us, why do we endanger ourselves every hour?
31I face death every day—yes, just as surely as I boast about you in Christ Jesus our Lord.
32If I fought wild beasts in Ephesus with no more than human hopes, what have I gained? If the dead are not raised,
Add the mysterious passage in verses 29-32 that nobody who believes in the popular false doctrines about resurrection would never have an answer to.
My take has always been, resurrection of saints is now and continuous until the end of age. The end of age is also called the day of the Lord or the coming of the Christ, but actually Christ is coming every day. There's not rapture at all, the souls of saints are resurrected immediately and indwell the hearts of living believers on earth. The living believers at the very end shall be shelved from death and it is they that their bodies will be turned into spiritual bodies in a twinkle of an eye.